Initializing the video display

    SDL_Surface *screen;

    /* Initialize the SDL library */
    if( SDL_Init(SDL_INIT_VIDEO) < 0 ) {
        fprintf(stderr,
                "Couldn't initialize SDL: %s\n", SDL_GetError());
        exit(1);
    }

    /* Clean up on exit */
    atexit(SDL_Quit);

    /* Initialize the display in a 640x480 8-bit palettized mode */
    screen = SDL_SetVideoMode(640, 480, 8, SDL_SWSURFACE);
    if ( screen == NULL ) {
        fprintf(stderr, "Couldn't set 640x480x8 video mode: %s\n",
                        SDL_GetError());
        exit(1);
    }

Initializing the best video mode

    /* Have a preference for 8-bit, but accept any depth */
    screen = SDL_SetVideoMode(640, 480, 8, SDL_SWSURFACE|SDL_ANYFORMAT);
    if ( screen == NULL ) {
        fprintf(stderr, "Couldn't set 640x480x8 video mode: %s\n",
                        SDL_GetError());
        exit(1);
    }
    printf("Set 640x480 at %d bits-per-pixel mode\n",
           screen->format->BitsPerPixel);

Loading and displaying a BMP file

    SDL_Surface *image;
    SDL_Rect dest;
    int ncolors, i;
    SDL_Color *colors;

    /* Load the BMP file into a surface */
    image = SDL_LoadBMP("sample.bmp");
    if ( image == NULL ) {
        fprintf(stderr, "Couldn't load sample.bmp: %s\n",
                        SDL_GetError());
        return;
    }

    /* Set the display colors -- SDL_SetColors() only does something on
       palettized displays, but it doesn't hurt anything on HiColor or
       TrueColor displays.
       If the display colors have already been set, this step can be
       skipped, and the library will automatically map the image to
       the current display colors.
    */
    if ( image->format->palette ) {
        ncolors = image->format->palette->ncolors;
        colors  = (SDL_Color *)malloc(ncolors*sizeof(SDL_Color));
        memcpy(colors, image->format->palette->colors, ncolors);
    } 
    else {
        int r, g, b;

        /* Allocate 256 color palette */
        ncolors = 256;
        colors  = (SDL_Color *)malloc(ncolors*sizeof(SDL_Color));

        /* Set a 3,3,2 color cube */
        for ( r=0; r<8; ++r ) {
            for ( g=0; g<8; ++g ) {
                for ( b=0; b<4; ++b ) {
                    i = ((r<<5)|(g<<2)|b);
                    colors[i].r = r<<5;
                    colors[i].g = g<<5;
                    colors[i].b = b<<6;
                }
            }
        }
        /* Note: A better way of allocating the palette might be
           to calculate the frequency of colors in the image
           and create a palette based on that information.
        */
    }
    /* Set colormap, try for all the colors, but don't worry about it */
    SDL_SetColors(screen, colors, 0, ncolors);
    free(colors);

    /* Blit onto the screen surface */
    dest.x = 0;
    dest.y = 0;
    dest.w = image->w;
    dest.h = image->h;
    SDL_BlitSurface(image, NULL, screen, &dest);

    SDL_UpdateRects(screen, 1, &dest);

    /* Free the allocated BMP surface */
    SDL_FreeSurface(image);
    return;

Drawing directly to the display

    /* Code to set a yellow pixel at the center of the screen */

    Sint32   X, Y;
    Uint32   pixel;
    Uint8   *bits, bpp;

    /* Map the color yellow to this display (R=0xFF, G=0xFF, B=0x00)
       Note:  If the display is palettized, you must set the palette first.
    */
    pixel = SDL_MapRGB(screen->format, 0xFF, 0xFF, 0x00);

    /* Calculate the framebuffer offset of the center of the screen */
    if ( SDL_MUSTLOCK(screen) ) {
        if ( SDL_LockSurface(screen) < 0 )
            return;
    }
    bpp = screen->format->BytesPerPixel;
    X = screen->w/2;
    Y = screen->h/2;
    bits = ((Uint8 *)screen->pixels)+Y*screen->pitch+X*bpp;

    /* Set the pixel */
    switch(bpp) {
        case 1:
            *((Uint8 *)(bits)) = (Uint8)pixel;
            break;
        case 2:
            *((Uint16 *)(bits)) = (Uint16)pixel;
            break;
        case 3: { /* Format/endian independent */
            Uint8 r, g, b;

            r = (pixel>>screen->format->Rshift)&0xFF;
            g = (pixel>>screen->format->Gshift)&0xFF;
            b = (pixel>>screen->format->Bshift)&0xFF;
            *((bits)+screen->format->Rshift/8) = r; 
            *((bits)+screen->format->Gshift/8) = g;
            *((bits)+screen->format->Bshift/8) = b;
            }
            break;
        case 4:
            *((Uint32 *)(bits)) = (Uint32)pixel;
            break;
    }

    /* Update the display */
    if ( SDL_MUSTLOCK(screen) ) {
        SDL_UnlockSurface(screen);
    }
    SDL_UpdateRect(screen, X, Y, 1, 1);

    return;

Fastest possible surface blit

There are three different ways you can draw an image to the screen:

The best way to do this is to combine methods:

#include <stdio.h>
#include <stdlib.h>
#include "SDL.h"
#include "SDL_timer.h"

void ComplainAndExit(void)
{
    fprintf(stderr, "Problem: %s\n", SDL_GetError());
    exit(1);
}

int main(int argc, char *argv[])
{
    SDL_PixelFormat fmt;
    SDL_Surface *screen, *locked;
    SDL_Surface *imagebmp, *image;
    SDL_Rect dstrect;
    int i;
    Uint8 *buffer;

    /* Initialize SDL */
    if ( SDL_Init(SDL_INIT_VIDEO) < 0 ) {
        ComplainAndExit();
    }
    atexit(SDL_Quit);

    /* Load a BMP image into a surface */
    imagebmp = SDL_LoadBMP("image.bmp");
    if ( imagebmp == NULL ) {
        ComplainAndExit();
    }

    /* Set the video mode (640x480 at native depth) */
    screen = SDL_SetVideoMode(640, 480, 0, SDL_HWSURFACE|SDL_FULLSCREEN);
    if ( screen == NULL ) {
        ComplainAndExit();
    }

    /* Set the video colormap */
    if ( imagebmp->format->palette != NULL ) {
        SDL_SetColors(screen,
                      imagebmp->format->palette->colors, 0,
                      imagebmp->format->palette->ncolors);
    }

    /* Convert the image to the video format (maps colors) */
    image = SDL_DisplayFormat(imagebmp);
    SDL_FreeSurface(imagebmp);
    if ( image == NULL ) {
        ComplainAndExit();
    }

    /* Draw bands of color on the raw surface */
    if ( SDL_MUSTLOCK(screen) ) {
        if ( SDL_LockSurface(screen) < 0 )
            ComplainAndExit();
    }
    buffer=(Uint8 *)screen->pixels;
    for ( i=0; i<screen->h; ++i ) {
        memset(buffer,(i*255)/screen->h,
               screen->w*screen->format->BytesPerPixel);
               buffer += screen->pitch;
    }
    if ( SDL_MUSTLOCK(screen) ) {
        SDL_UnlockSurface(screen);
    }

    /* Blit the image to the center of the screen */
    dstrect.x = (screen->w-image->w)/2;
    dstrect.y = (screen->h-image->h)/2;
    dstrect.w = image->w;
    dstrect.h = image->h;
    if ( SDL_BlitSurface(image, NULL, screen, &dstrect) < 0 ) {
        SDL_FreeSurface(image);
        ComplainAndExit();
    }
    SDL_FreeSurface(image);

    /* Update the screen */
    SDL_UpdateRects(screen, 1, &dstrect);

    SDL_Delay(5000);        /* Wait 5 seconds */
    exit(0);
}